This invention relates to a device for automatically positioning the optical head of a surgical microscope relative to the operating site.
Microsurgical techniques and methods are widespread in many specialist sectors of medical science, such as neurosurgery, ophthalmology, reconstructive hand and foot surgery, etc. The common denominator is the use of an optical microscope in the operating theater for suitably magnifying the anatomical details of the part subjected to surgery.
An operating microscope consists essentially of an objective and a pair of "tube lenses". When the object to be observed is placed in the focal plane of the objective, these lenses reproduce an intermediate image of it which can be observed and/or magnified by a pair of oculars. Tube lenses and oculars are provided as a pair to allow the object to be viewed stereoscopically.
Normally between the objective and tube lenses there is inserted a revolving turret with Galilean telescopes or a pancratic system to be able to vary, respectively discretely or continuously, the resultant total magnification of the microscope. Typical magnifications are between 5 and 50. Frequently the magnification system is operated by a motorized system, suitably controlled by a keypad.
The optical head of the microscope is completed by a coaxial illumination system for the operating field. The optical head is mechanically suspended from an articulated arm rigid with a stand rigidly connected to the ceiling or to a suitable base rigid with the floor. To be able to be freely positioned over the operating couch, the microscope is provided with a system for fine translation in the vertical direction (for focusing) and in the two horizontal directions (for image centering). Frequently such movements are effected by electric motors controlled by a pedal board available to the surgeon.
The microscope optical head can be provided with an image divider, making a further two observation channels available. It is normal practice to install an additional pair of oculars for use by a second operator and a photographic or television apparatus for acquiring visual documentation of the microsurgery.
Using a modular system it is possible in reality to install on the same microscope a number of image dividers, and to connect to each of them either an additional pair of oculars or a photographic, television or other apparatus which can be considered useful. It should be noted that the field of vision on the recording channel is usually smaller than that available to the primary operator, because of the different configuration of the optical systems forming the image. This means that the microscope objective must be centered as accurately as possible on the zone of interest to the operation. In this respect, where the surgeon is still able to "see", it is not automatically certain that the eye of the telecamera or photographic apparatus is able to receive a sharp and reproducible image.
If the area of surgical interest leaves the field of vision of the operator, or of the recording system (for example reproduced on a monitor by a telecamera), the surgeon himself or herself, or rather one of his or her assistants, operates the translation motors to return the image of interest to the center of the field of vision. This is not always easy, and in particular could take too much time. It can hence happen that the surgeon loses vision of the field of operating interest for a few moments, with consequent obvious inconvenience, or the loss of important operating stages in the archive of photographic images or visual recording.
The fact of the area of surgical interest leaving the field of vision of the operator can have various causes. In general it can happen either because the site of the surgical treatment has effectively changed or because, although this site has remained unchanged, that part of the body on which the operation is being carried out has shifted for strictly anatomical reasons.
A typical surgical operation in which this often happens is vitreo-retinal endoscopic surgery, in which the field of operation is the rear chamber of the eyeball.
During vitreo-retinal endoscopic operations, the surgeon introduces into the eyeball not only the operating instruments but also, according to requirements, draining or infusion probes, or lighting systems such as a fiber optic endoscopic probe.
In this type of operation, the entire part on which surgery is to be carried out cannot always fall within the visual and recording field of the microscope. This is even more so the case when operating with high magnification. It often happens that the position of the microscope optical head has to be readjusted as a result of the shifting of the operation site. Again, because of the anatomy of the organ subjected to surgery (i.e. the eyeball) and of the considerable freedom of rotation of the eyeball within its socket, it can happen that although the surgery remains on the same portion of tissue, the eyeball undergoes considerable rotation within its socket, for example because of surgical maneuvers by the surgeon. This can shift the image of interest outside the field of vision.
Given the relative frequency of such movements, reiterated adjustments of the microscope position are required, to the detriment of the attention and comfort of the surgeon, in addition to the detriment of the quality of the images being acquired.